The present invention relates generally to channel estimation in mobile communication networks and, more particularly, to channel estimation with multiple control channels for high data rate transmission.
Wideband Code Division Multiple Access (WCDMA) Systems are merging as a leading global Third Generation (3G) standard for mobile communication networks. 3GPP Release 6 of the WCDMA standard introduced a number of enhancements in the uplink including fast scheduling and hybrid ARQ with soft combining in order to achieve higher data rates in the uplink. To support the enhancements to the uplink, Release 6 introduced a new transport channel called the Enhanced Dedicated Channel (E-DCH) which corresponds to a set of separate channelization codes for data and associated control signaling. The Enhanced-Dedicated Physical Data Channel (E-DPDCH) carries the data. Depending on the data rate, the number of E-DPDCHs and their spreading codes are varied. The Enhanced Dedicated Physical Control Channel (E-DPCCH) is used to indicate the transport block format (e.g., E-TFCI symbols), which is needed to demodulate and decode signals transmitted on the E-DPDCHs. The E-DPCCH carries also information for Hybrid Automatic Repeat-reQuest (ARQ) and scheduling.
In Release 7 higher order modulation (16 QAM in the uplink) was introduced to improve the peak data rate. Higher data rates are achieved at high signal-to-noise ratios. To ensure reliable demodulation at these higher data rates, the Dedicated Physical Control Channel (DPCCH), which carries the pilot symbols used for channel estimation, need to be transmitted at higher power. However, increasing the transmit power on the DPCCH increases the amount of interference to other users and reduces system capacity.
To avoid increasing the transmit power on the DPCCH for high data rate users, the E-DPCCH may be used as a pilot signal for channel estimation. Release 7 of the WCDMA standard introduced a new operating mode, referred to herein as the boosted E-DPCCH mode, wherein the transmit power on the E-DPCCH is boosted at high data rates to enable the E-DPCCH to be used as a pilot signal. Because the E-DPCCH is transmitted only when the E-DPDCH is transmitted, the E-DPCCH causes less interference than caused by increasing the transmit power on the DPCCH, which is transmitted more frequently. During normal operation, the base station usually uses only the pilot symbols transmitted on the DPCCH for channel estimation. When operating in the boosted E-DPCCH mode, channel estimation from DPCCH may not be reliable.